EIS 2.2 Scaling of the Sun, Earth, Moon System

Table 1 Size & Distance Comparison of the SEM Solar System Body Distance from Earth (km) Earths Away Diameter (km) Earths Across Sun150,000,000~ 12,0001,392, Moon384,000303, Earth Equator = 12,756 1

I. Moon 1. Age ~ billion years old, a bit younger than Earth 2. When a Mars-sized rock hit Earth, debris traveled at just the right speed to stay in orbit around Earth to create the Moon. 3. Has no atmosphere, so no weather. 4. Diameter ~ ¼ of Earth’s diameter 5. Since it rotates at the same rate it revolves around Earth, we only see one side of the Moon – EVER.

II. Day 1. Caused by Earth rotating on its axis once every 24 hours (about – takes slightly longer)

III. Month 1. Sidereal Month: The time it takes Moon to revolve around Earth & be next to same background star days to go from Point A back to Point A 27.3 days to go from Point A back to Point A 2. Synodic Month: The time it takes Moon to revolve around Earth and be in the same phase (it’s longer b/c Earth is moving-so Moon is playing catch up to get to the same phase) 29.5 days to go from, say, full Moon to full Moon 29.5 days to go from, say, full Moon to full Moon

IV. Year 1. Caused by Earth taking ~ 365 ¼ days to revolve around the Sun. 2. We don’t add 6 hours to the clock every year. Instead we add a whole day, February 29 th, every 4 years.

IV. Year (don’t need to copy) 1. Some exceptions to this rule are required since the duration of a solar year is slightly less than days. In the Gregorian calendar, the calendar used by most modern countries, the following three criteria determine which years will be leap years:

IV. Year (don’t need to copy) i. Every year that is divisible by four is a leap year ii. Of those years, if it can be divided by 100, it is NOT a leap year, UNLESS iii. The year is divisible by 400. Then it IS a leap year. iv. So, years 1800, 1900, 2100, 2200, 2300, and 2500 are NOT leap years, while 1600 & 2000 ARE leap years.

V. The Sun 1. It is one of 200 billion stars in the Milky Way galaxy 2. It (& our solar system) revolves around center of galaxy at ½ a million miles per hour! ~ 200 million years to go around once! 3. It is 400 times larger than Moon & 400 times farther away, so Sun & Moon appear same size in sky million Earth’s would fit inside Sun.